Move isValid/isCurrentColor from Color to StyleColor

Source/core/page/FrameView.h

Index: Source/core/page/FrameView.h
diff --git a/Source/core/page/FrameView.h b/Source/core/page/FrameView.h
index fad036e924112d43d619f125f534ff9a7b231fb5..ff021cf007f9659f1daf79d2159ae7c9807b55b5 100644
--- a/Source/core/page/FrameView.h
+++ b/Source/core/page/FrameView.h
@@ -141,8 +141,8 @@ public:
     bool hasOpaqueBackground() const;
 
     Color baseBackgroundColor() const;
-    void setBaseBackgroundColor(const Color&);
-    void updateBackgroundRecursively(const Color&, bool);
+    void setBaseBackgroundColor(const StyleColor&);
+    void updateBackgroundRecursively(const StyleColor&, bool);
 
     bool shouldUpdateWhileOffscreen() const;
     void setShouldUpdateWhileOffscreen(bool);
@@ -233,7 +233,7 @@ public:
     virtual void paintScrollCorner(GraphicsContext*, const IntRect& cornerRect);
     virtual void paintScrollbar(GraphicsContext*, Scrollbar*, const IntRect&) OVERRIDE;
 
-    Color documentBackgroundColor() const;
+    StyleColor documentBackgroundColor() const;
 
     static double currentPaintTimeStamp() { return sCurrentPaintTimeStamp; } // returns 0 if not painting